So it seems Katherine's life is coming to an end due to old age. So far they made it clear that the cure made her unable to become a vampire again. So currently, the only available option left for Katherine seems to be Nadia's suggestion, traveler's magic to allow her to live on in someone else's body after she dies. However, being identical in appearance seem to be the main point for Elena and Katherine, so it doesn't seem like the writers would actully put Katherine is somebody else, and if they put her in Elena, it would be really messed up.
Klaus is going to show up in the next TVD epsiode which Katherine is dying, maybe this hints he'll have a part in extending Katherine's life, but it's hard to imagine how, unless his hybrid blood can somehow help Katherine. But they've pretty much established that hybrid blood affects human bodies no different than vampire blood would, unless they want to introdcue something new about hybrid blood, or how Katherine's condition can be improved by it.
Anyone has any speculation to sure whether this is finally the end for Katherine or she will again survive somehow?